What is pyre-check?

Pyre is a type checker for Python, built by Facebook. Python lets you write code without declaring what kind of data each variable holds, but you can add optional type hints to your code to describe that. Pyre reads those hints and flags any places where the actual data does not match what the hints say, catching a category of bugs before the code ever runs. It is built to be fast on large codebases. Rather than re-checking everything from scratch each time, it runs a background process that watches for file changes and updates its analysis incrementally, so checking a file after a small edit happens almost instantly even in a project with millions of lines of code. Pyre also ships with a companion tool called Pysa, which focuses on security. Pysa traces how data flows through a Python application and flags cases where untrusted input might reach a sensitive operation, such as a database query or a shell command, a class of bugs known as injection vulnerabilities. The README includes a note that a next-generation successor called Pyrefly is now available at a separate repository, and that Pyre itself is no longer the primary active development focus. For new projects, the maintainers point to Pyrefly instead. Pyre requires Python 3.9 or later and a file-watching tool called Watchman to run.